The availability of tryptophan (TRP) and tyrosine (TYR) to the brain influences serotonin (5HT) and catecholamine (CAM) synthesis, respectively. Diet and the ingestion of single meals modify TRP and TYR uptake into brain, and thus 5HT and CAM formation. Diet may therefore also modify transmitter release, and accordingly influence brain outputs (e.g, particular behaviors and neuroendocrine secretions). Few studies have explored the potential relationships among diet, brain neurotransmitters, and behavior-neuroendocrine function. The proposed research program will study whether diet-induced modifications in brain neurotransmitter synthesis lead to changes in behaviors and hormonal secretions that have been shown most clearly to correlate with the activity of 5HT and CAM neurons in brain. In particular, we will study (1) pain sensitivity in rats, using foot shock (i.e., flinch-jump test), (2) sleep in normal human subjects, by recording sleep EEG activity, (3) food intake regulation in rats allowed to select the amounts of protein they consume each day, and (4) pituitary hormone secretions in rats bearing chronic indwelling atrial cannulae. Growth hormone and prolactin secretion will be studied in these animals, from which samples can be drawn at 15 minute intervals. Finally, although most studies will focus on 5HT and CAM, we will also explore whether choline-induced changes in brain acetylcholine formation influence the brain outputs under investigation. The results of this line of experimentation, aside from elucidating potentially-important mechanisms by which the external environment influences brain function, could also aid in the management of certain disease states involving altered synthesis and/or release of 5HT, CAM, or acetylcholine (e.g., depression), by providing simple dietary treatments or adjuncts to drug therapy for helping to correct the neurotransmitter imbalance.